Re: [PATCH v2] ath11k: fix a locking bug in ath11k_mac_op_start()

[Kalle Valo <kvalo@codeaurora.org>]

Dan Carpenter <dan.carpenter@oracle.com> writes:

> This error path leads to a Smatch warning:
>
> 	drivers/net/wireless/ath/ath11k/mac.c:4269 ath11k_mac_op_start()
> 	error: double unlocked '&ar->conf_mutex' (orig line 4251)
>
> We're not holding the lock when we do the "goto err;" so it leads to a
> double unlock.  The fix is to hold the lock for a little longer.
>
> Fixes: c83c500b55b6 ("ath11k: enable idle power save mode")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> v2: reviewers were concern that v1 was racy
>
>  drivers/net/wireless/ath/ath11k/mac.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath11k/mac.c b/drivers/net/wireless/ath/ath11k/mac.c
> index c1608f64ea95..464d3425488b 100644
> --- a/drivers/net/wireless/ath/ath11k/mac.c
> +++ b/drivers/net/wireless/ath/ath11k/mac.c
> @@ -4248,8 +4248,6 @@ static int ath11k_mac_op_start(struct ieee80211_hw *hw)
>  	/* Configure the hash seed for hash based reo dest ring selection */
>  	ath11k_wmi_pdev_lro_cfg(ar, ar->pdev->pdev_id);
>  
> -	mutex_unlock(&ar->conf_mutex);
> -
>  	rcu_assign_pointer(ab->pdevs_active[ar->pdev_idx],
>  			   &ab->pdevs[ar->pdev_idx]);
>  
> @@ -4262,6 +4260,9 @@ static int ath11k_mac_op_start(struct ieee80211_hw *hw)
>  			goto err;
>  		}
>  	}
> +
> +	mutex_unlock(&ar->conf_mutex);
> +
>  	return 0;
>  
>  err:
> -- 
> 2.30.0

But now rcu_assign_pointer() is called while conf_mutex is held,
previously it was not. I didn't check if this creates problems, but just
to be on the safe side I modified your patch to keep the original
functionality. Please check my changes in the pending branch:

https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&idŽff3667c211072a2107271139b81cbf8c7fd10a

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